This invention relates generally to the preparation of tissue specimens, and in particular to forming and freezing tissue specimens while preserving a desired orientation of the specimen.
Various disease processes, particularly tumors, require a histologic diagnosis. Preparation of tissue specimens for rapid histological examination requires the preservation of the integrity and spatial positioning of the tissue specimen. Tissue integrity and spatial positioning relative to the eventual cutting plane of a microtome are important for histological evaluation of the appropriate areas and their relationship to margins and other structures. If the relevant areas of the tissue do not lie on the same plane, then several sections of the tissue must be taken and made into separate slides for evaluation. Each of these different slides will have a different part of the original tissue sample and will need to be separately evaluated by the pathologist. Pathologic examination can be significantly improved and the cost reduced if a single slide of the tissue can include all of the relevant areas that need evaluation in the biopsy including the abnormal tissue and the margins.
Biopsy, or surgical removal of a tissue specimen for histologic examination, is frequently employed in order to establish a precise diagnosis. When a lesion is known or suspected to be malignant, the entire mass is typically excised, if possible, and a rapid examination technique is often employed to determine tumor relationship to margins. In some circumstances to be effective, the technique of tumor margin surface area examination must include microscopic examination of the entire surface margin of the excised specimen. Moreover, the anatomical orientation of the tissue must be maintained throughout the procedure so that the surgeon may be directed back to a specific area of the biopsy site to excise additional tissue until histologic examination indicates that only healthy cells remain. Frozen section examination requires that the tissue first be prosected and oriented, hard frozen, and then sliced into extremely thin sections for microscopic examination.
In order to speed the examination process, the specimen must be quickly frozen to a predetermined temperature, mounted on a microtome chuck which will permit the frozen tissue to be thin sliced in a cryostat/microtome. The invention allows more precise orientation of larger, non-planar specimens, faster than current methods.
Prior art methods for freezing tissue with a desired orientation, include direct placement of the tissue sample on a cryostat chuck, placement of a freezing gel on the tissue sample, and using the cryostat anvil to apply a freezing temperature to the tissue sample. Another method is the use of a disposable plastic mold. The tissue and an aqueous solution are placed in a plastic mold. The mold and contents are then frozen within a cryostat. In both prior art methods, it is difficult to keep the tissue sample in a desired orientation. Furthermore, the plastic mold provides some heat insulation and will delay the specimen freezing process.
The apparatus and method of the present invention are specifically designed to quickly form and freeze a tissue specimen into a desired frozen block, while preserving a desired orientation of the specimen.